<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        #box
        {
            border: 3px solid blue;
            width: 300px;
            height: 200px;
        }
        #ball
        {
            width: 10px;
            height: 10px;
            border-radius: 50%;
            position: absolute;
            background-color: yellow;
            border: 1px solid blue;
        }
    </style>
</head>
<body>
    <div id="box">
        <div id="ball"></div>
    </div>
    <script src="movingball.js"></script>
</body>
</html>